The present invention is related to disc drive data storage systems and, more particularly, to an apparatus and method for actively controlling curvature of a transducing head, such as a hydrodynamic bearing slider.
A typical hard disc drive includes one or more rigid discs coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective head gimbal assemblies (HGAs). Head gimbal assemblies carry transducers which write information to and read information from the disc surface. An actuator mechanism moves the head gimbal assemblies from track to track across the surfaces of the discs under control of electronic circuitry.
The head gimbal assembly includes a gimbal (or flexure) and a slider. The gimbal provides a resilient connection that allows the slider to pitch and roll while following the topography of the disc. The slider includes a slider body having a bearing surface, such as an air bearing surface, which faces the disc surface. As the disc rotates, the air pressure between the disc and the air bearing surface increases, which creates a hydrodynamic lifting force that causes the slider to lift and fly above the disc surface. The transducer is typically mounted at or near the trailing edge of the slider
In some applications, the slider flies in close proximity to the surface of the disc. This type of slider is known as a xe2x80x9cpseudo-contactxe2x80x9d slider, since the bearing surface of the slider can occasionally contact the surface roughness of the disc. In other applications, the slider is designed to remain in direct contact with the disc surface with substantially no air bearing. These sliders are referred to as xe2x80x9ccontact recordingxe2x80x9d sliders.
It is often desirable to fabricate a slider such that the bearing surface has a positive curvature along the length and width of the slider. Length curvature is known as crown curvature. Width curvature is known as cross or camber curvature. The proper setting and control of crown and cross curvature improves fly height variability over varying conditions, improves wear on the slider and the disc surface, and improves takeoff performance by reducing stiction between the slider and the disc surface. In addition, the slider preferably has no twist about its longitudinal or transverse axes.
Curvature has been controlled in the past by lapping the bearing surface on a spherically-shaped lapping surface or on a flat lapping surface while rocking the slider body back and forth in the direction of the desired curvature. The amount of curvature is determined by the radius of the rocking rotation. This lapping process is difficult to control and results in large manufacturing tolerances. U.S. Pat. Nos. 5,442,850; 5,266,769; 5,982,583 and 6,073,337 disclose various other methods for setting slider curvature by altering surface stresses in the slider body material during fabrication of the slider body. The curvature of the slider is then fixed after fabrication.
However, increased hard disc drive recording density has been associated with a drastic decrease in a slider""s fly height. In addition, media roughness or media xe2x80x9cglide avalanchexe2x80x9d, a geometrical parameter used to qualify topography of media surface in production, has been significantly decreased. As a result, controlling fly height and measuring or qualifying media topography in a reliable manner have become more challenging. Media glide avalanche is typically measured with a glide head that is sensitive to contact with media defects and flies at a height comparable to the media glide avalanche. Recording heads usually fly at a greater height from the disc surface than a corresponding glide head.
Instead of relying on optimized passive, air bearing surfaces and fabricated crown curvatures to control slider fly heights, various approaches to actively control slider fly height during operation of a data storage system have been proposed both for recording heads and glide heads. U.S. Pat. No. 5,021,906 discloses a method of controlling slider fly height in which a central region of a conventional slider is deformed using a layer of piezoelectric material. However, conventional air bearing designs have been driven by the desire to minimize fly height sensitivity to manufacturing variations, including crown curvature. Thus, usefulness of this technique of actively controlling fly height by varying crown curvature has been limited.
An improved method and apparatus are desired for actively controlling slider fly height during operation of the disc drive.
In one aspect of the invention, a slider is provided for actively controlling the fly height of the slider relative to a data storage disc. The slider includes a slider body with front and back surfaces, a length and a crown curvature on the front surface along the length. In addition, first and second elongated rails positioned on the front surface form first and second bearing surfaces, respectively. Each of the bearing surfaces includes a leading portion, a trailing portion and a waist portion, wherein the waist portion is wider than the leading and trailing portions and has a maximum width within a middle half of the length of the slider body. A deformable material is positioned on the slider body and has a dimension that is changeable in response to an electrical control signal applied to the deformable material wherein a change in the dimension causes a change in the crown curvature.
Another aspect of the invention relates to a disc drive data storage system having a disc and a disc head slider. The disc is rotatable about a central axis and has a recording surface. The disc head slider carries a transducer at a fly height relative to the recording surface during rotation of the disc, wherein the fly height is sensitive to changes in a crown curvature of the disc head slider. The crown curvature of the disc head slider is actively altered in order to adjust the fly height during rotation of the disc, wherein an increase in the crown curvature causes an increase in the fly height.
Another aspect of the invention relates to a method for actively modifying a fly height of a transducer relative to a data storage disc. The method includes carrying the transducer with a slider, wherein the slider has front and back surfaces and a crown curvature along the front surface. The method further includes rotating the data storage disc relative to the slider and altering the crown curvature of the slider during rotation. Using this method, a positive change in the crown curvature results in a positive change in the fly height and a negative change in the crown curvature results in a negative change in the fly height.